Method for enantioselective hydrogenation of chromenes

ABSTRACT

A method for preparing an enantiomeric chromane, by asymmetrically hydrogenating a chromene compound in the presence of an Ir catalyst having a chiral ligand. The method includes the enantioselective preparation of enantiomeric equol. A preferred Ir catalyst has a chiral phosphineoxazoline ligand. Enantiomeric chromanes of high stereoselective purity can be obtained.

BACKGROUND OF THE INVENTION

Isoflavones and many derivatives thereof possess a wide range ofimportant biological properties including estrogenic effects.Isoflavanoids found in soy, such as genistein and daidzein, have alsoattracted interest as dietary phytoestrogens that might be effective forthe treatment of hormone-dependent conditions and diseases. In examiningthe impact of the estrogenic activity of soy isoflavones (commonlyreferred to as phytoestrogens), one needs to consider not only theisoflavones and their conjugates that are ingested, but alsobiologically active metabolites that might be generated from the invivo. Daidzein, in isoflavone in soy, can be converted to thecorresponding chromane S-(−)equol, a compound with greater estrogenicactivity than its precursor (see K. D. R. Setchell, N. M. Brown, E.Lydeking-Olsen. J. Nutrition, 2002, 132/12, pp 3577-3584). Thisreductive metabolic conversion is the result of the action ofequol-producing gut microflora found in a proportion of the humanpopulation who are known as “equol producers”. Equol was first isolatedfrom pregnant mare's urine in 1932 and was subsequently identified inthe plasma of sheep (derived from formononetin found in red cloverspecies). In 1982 it was first identified in human urine. Equol is achiral center and therefore can exist in two enantiomeric forms. It hasbeen recently established that S-(−)equol is the enantiomer produce bythe metabolic reduction of isoflavones ingested by humans (see SetchellK D R, Clerici C, Lephart E D, Dole S J, Heenan, C, Castellani D, WolfeB, Nechemias L-Z, Brown N, Baraldi G, Lund T D, Handa R J, Heubi J E.S-Equol, a potent ligand for estrogen receptor-beta, is the exclusiveenantiomeric form of the soy isoflavone metabolite produced byintestinal bacterial flora. American Journal of Clinical Nutrition 2005;81:1072-1079.

A convenient preparation of racemic (+) equol(7-hydroxy-3-(4′-hydroxyphenyl)-chroman) based on transfer hydrogenationif daidzein was published (K. Wahala, J. K. Koskimies, M. Mesilaakso, A.K. Salakka, T. K. Leino, H. Adlercreutz. J. Org. Chem., 1997, v 62, p7690-7693), and more recently by J. A. Katzenellenbogen et al.(Bioorganic & Medicinal Chem., 2004, 12, pp 1559-1567). A procedure isknown for isolation of enantiomeric S- and R-equol from the racemicmixture by chiral chromatographic resolution of (+) equol using aβ-cyclodextrin column (see PCT Publication WO03/23056, published Jan.29, 2004, and incorporated herein by reference). However, this approachhas certain production rate limitations, and may not be suitable formaking commercial quantities of enantioselective equol.

Therefore, a need remains to develop a cost-effective method ofsynthesizing commercial quantities of enantioselective equol and relatedenantioselective chromanes.

SUMMARY OF THE INVENTION

The present invention relates to a method for synthesizingenantioselective equol in high purity and yield. The invention isachieved by enantioselective hydrogenation of non-functionalized cyclicolefins, and in particular, chromenes.

The present invention also relates to a method for preparingenantioselectively an enantiomeric chromane (compound (I)):

wherein each R⁴, R⁵, R⁶, and R⁷ is independently selected from the groupconsisting of H, OH, phenyl, aryl, alkyl, alkylaryl, arylalkyl, OR⁸,OC(O)R⁸, OS(O)R⁸, thio, alkylthio, mercaptal, alkylmercaptal, amino,alkylamino, dialkylamino, nitro and halo, and where R⁸ is alkyl andalkylaryl; and R¹, R2, and R³ is independently selected from —R⁴ and

wherein each R⁹, R¹⁰, R¹¹, R¹², and R¹³ is independently selected from Hand R⁴; comprising the steps of:

1) providing a chromene compound selected from:

2) hydrogenating the chromene in the presence of an Ir catalyst having achiral ligand shown as compound (V):

to form the chromane; wherein each of Y and X is independently selectedform the group consisting of S, O and N, and each R¹⁴ and R¹⁵ isindependently selected from the group consisting of alkyl, aryl, phenyl,alkylaryl, and arylalkyl.

The invention also relates to a method for preparing enantioselectivelyan enantiomeric equol or (compound (VI)):

wherein Z is H or PG, wherein PG is a hydroxyl protective group;comprising the steps of:

1) providing a 3-phenylchromene compound selected from:

and

2) hydrogenating the 3-phenylchromene in the presence of an Ir catalysthaving a chiral ligand shown as compound (V):

to form an enantiomeric equol, wherein each of Y and X is independentlyselected from the group consisting of S, O and N, and each R¹⁴ and R¹⁵is independently selected from the group consisting of alkyl, aryl,phenyl, alkylaryl, and arylalkyl. When 3-phenylchromene compound isprotected (X is PG), the protected enantiomeric equol compound (VI) canoptionally be converted (for example: by acidification) to theenantiomeric equol, and analogs thereof.

The invention further relates to a method of preparingenantioselectively an enantiomeric equol, and analogs thereof,comprising the steps of: 1) reducing a 3-phenyl chromen-4-one to itscorresponding chroman-4-one; 2) reducing the chroman-4-one to acorresponding chroman-4-ol; 3) dehydrating the chroman-4-ol to acorresponding chromene selected from 3-phenyl-3,4 chromene and3-phenyl-2,3 chromene; and 4) hydrogenating the chromene in the presenceof an Ir catalyst of compound (V) having a chiral ligand, to form theenantiomeric equol, and analogs thereof.

The invention further relates to the synthesis of enantioselectivechromans, including enantiomeric equol, containing stable-isotopic atomsof ¹³C, ¹⁸O, or ²H, where such atoms are introduced in one of theintermediate steps in the preparation of the intermediate chromene orenantioselective chromane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C and 1D show the Gas Chromatography Mass Spectrometry(GC-MS) trace and spectra, and the Liquid Chromatography Massspectrometry (LC-MS) trace and spectra, respectively, on a bis-MOMdaidzein intermediate product in accordance with the present invention.

FIGS. 2A, 2B, 2C and 2D show the GC-MS trace and spectra, and the LC-MStrace and spectra, respectively, on a chroman-4-one intermediate productin accordance with the present invention.

FIGS. 3A, 3B, 3C and 3D show the GC-MS trace and spectra, and the LC-MStrace and spectra, respectively, on a chroman-ol product intermediateproduct (dehydrated) in accordance with the present invention.

FIGS. 4A, 4B, 4C and 4D show the GC-MS trace and spectra, and the LC-MStrace and spectra, respectively, on a bis-MOM-dehydroequolintermediate/product in accordance with the present invention.

FIGS. 5A, 5B, 5C and 5D show the GC-MS trace and spectra, and the LC-MStrace and spectra, respectively, on a MOM-protected S-equol product inaccordance with the present invention.

FIGS. 6A and 6B show the LC-MS trace and spectra, respectively, on aS-equol product in accordance with the present invention.

FIGS. 7A, 7B, 7C and 7D show the GC-MS trace and spectra, and the LC-MStrace and spectra, respectively, on a MOM-protected R-equol product inaccordance with the present invention.

FIGS. 8A and 8B show the LC-MS trace and spectra, respectively, on aR-equol product in accordance with the present invention.

FIGS. 9A and 9B show the GC-MS trace and spectra, respectively, on aTMS-derivatized S-equol products in accordance with the presentinvention.

FIGS. 9C and 9D show the GC-MS trace and spectra, respectively, on aTBDMS-derivatized S-equol products in accordance with the presentinvention.

FIGS. 10A and 10B show the GC-MS trace and spectra, respectively, on aTMS-derivatized R-equol products in accordance with the presentinvention.

FIGS. 10C and 10D show the GC-MS trace and spectra, respectively, on aTBDMS-derivatized R-equol products in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

The term “enantioselective” refers to a chemical reaction thatpreferentially results in one enantiomer relative to a secondenantiomer, i.e., gives rise to a reaction product of which oneenantiomer, usually the desired enantiomer, has at least 10% of anenantiomeric excess (ee) in the reaction product.

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.For example, the phrase “optionally substituted” means that anon-hydrogen substituent may or may not be present on a given atom, and,thus, the description includes structures wherein a non-hydrogensubstituent is present and structures wherein a non-hydrogen substituentis not present.

Enantioselective Hydrogenation of Chromene

An embodiment of the invention provides a method for preparing achromane or substituted chromane having a chiral carbon contained withinthe heterocyclic ring and having a stereospecific configuration. Ageneral structure of the resulting chromane compound is represented bycompound (I), described herein before.

The chromane compound (I) illustrates substitution of the chromane withR² at the C-3 carbon position in the ring, such that only the C-3 carbonhas chirality. In this case, when R² is a non-hydrogen substituent andonly the C-3 carbon has chirality, then R¹ and R3 are H. Thestereospecific configuration of the synthesized compound (I) at itschiral center (the C-3 carbon position) can be dictated by thestereospecific configuration of the chiral ligand of the iridiumcatalyst, which typically has at least one, and more typically two, ormore, chiral carbon centers in the catalyst ligand, and by the type andmolecular weight of any non-hydrogen substituents R¹, R² and R³.

The starting compound for the chiral-selective hydrogenation is acorresponding chromene selected from compound (III) and (IV), describedherein above.

Alternatively, the chromene compounds (III) or (IV) can be substitutedwith a non-hydrogen substituent at either the C-4 position (R³) or atthe C-2 position (R¹), providing alternatively chirality at the C-4position or the C-2 position, respectively. When R¹ is a non-hydrogensubstituent and only the C-2 carbon has chirality, then R² and R³ are H;and when R³ is a non-hydrogen substituent and only the C-4 carbon haschirality, then R¹ and R² are H.

The selected chiral catalyst system comprises an enantioselectiveiridium catalyst comprising a chiral ligand shown herein before ascompound (V).

A more typical iridium-based catalyst comprises a chiralphosphine-oxazoline ligand of compound (IX), where R¹⁴ and R¹⁵ areearlier defined:

A preferred ligand compound is used wherein R¹⁴ is phenyl and R¹⁵ ismethyl.

The phosphine-oxazoline ligand having a (4S,5S) configuration in theoxazoline ring can be synthesized from the starting material L-threonine(2S,3R) by the method described by in Theonine-DerivedPhosphinite-Oxazoline Ligands for the Ir-Catalyzed EnantioselectiveHydrogenation, Adv. Synth. Catal., 2002, 344, pg. 40-44 (Menges andPfaltz), incorporated herein by reference, and is available from StremChemical, Newburyport, Mass. The phosphine-oxazoline ligand having a(4R,5R) configuration in the oxazoline ring can be synthesized by theMenges and Pfaltz method where the starting material L-threonine isreplaced with D-threonine (2R,3S).

The method has been shown to be highly stereospecific, typically formingenantiomeric chromanes having an enantiomeric excess (ee) of at least10%, more typically at least 50%, more typically at least 90%, and evenmore typically at least 95%, and up to 100%, more typically up to 99.5%,and more typically up to 99%.

Prior to hydrogenation of the chromene compound (III) or (IV), any ofR¹, R², R³, R⁴, R⁵, R⁶, or R⁷, which are hydroxyl, can be protected witha hydroxyl protecting group PG. A typical protective group,methoxymethyl (-MOM) is employed by refluxing the early stage chromeneprecursors such as daidzein with methoxy methylchloride in the presenceof diisopropyl ethyl amine. In other embodiments of the presentinvention, the chromene having unprotected hydroxyl substituents can beasymmetrically hydrogenated, typically in a polar solvent that improvesthe solubility of the unprotected chromene, such as, by example andwithout limitation, ethyl acetate, methanol, THF, N-methylpyrrolidone(NMP), dimethylformamide (DMF) and acetic acid.

Following hydrogenation, the protective group can be removed byacidification (for example, by excess HCl in methanol at between 0°C.-room temperature for 2 hours). Other acidic hydrolytic reagents (e.gacetic acid TFA as examples) can be used with differing rates of releaseof the protecting group. This step is also referred to as deprotectingof the compound.

The hydrogenation of the chromene is conducted in a polar solvent(typically dichloromethane) in hydrogen at pressures typically up to 200psig, and at ambient temperature or higher. The reaction proceedsrapidly (within minutes) at catalyst concentrations of at least about0.1 mol %, more typically at least about 0.5-2 mol %, and typically upto about 5 mol %, relative to the chromene.

Following enantioselective hydrogenation, the resulting enantiomericchromane can be isolated from solvent, reactants and catalyst, andpurified by chromatography on a silica gel plug filter, by procedureswell known to those skilled in the art. The structure of the product canbe confirmed by ¹H and ¹³C NMR analysis and by mass spectrometry withallied chromatography. The stereospecificity of the product can beconfirmed by optical dichroism.

Enantiospecific Hydrogenation of 3-phenylchromene to PrepareEnantiomeric Equol

In yet another embodiment of the invention, the method provides forpreparation of an enantiomeric equol(7-hydroxy-3-(4′-hydroxyphenyl)-chroman).

The starting compound for the chiral-selective hydrogenation is acorresponding protected or unprotected 3-phenyl chromene selected from:

wherein Z is H or PG, wherein PG is a hydroxyl protective group, andwherein the hydroxyl groups at the C-7 position on the chromene and atthe C-4 position of the 3-phenyl substituent have been protected,wherein PG is a hydroxyl protective group.

The selected chiral catalyst system comprises an iridium-based catalysthaving a ligand shown as compound (III), described above. A more typicaliridium-based catalyst comprises a phosphine-oxazoline ligand shownherein before as compound (IX). The preferred ligand is the compoundshown herein before as compound (X).

Typical solvents that can be used in the synthesis include a lower alkyldihalide such as dichloromethane, THF, and ethyl acetate. Other optionalsolvents, alone or in combination, include dimethylformamide (DMF),acetic acid, N-methylpyrrolidone (NMP), and methanol. Typically thereaction proceeds to completeness in dichloromethane at temperatures inthe range of 0 to room temperature (rt), within a time period of 1 minto 3 hours and the hydrogen pressure from 0 psig (bubbling hydrogenthrough the mixture) up to 150 psig.

The literature discloses that the use of the (4S,5S)-phospine-oxazolineligand in the synthesis using functionalized linear alkenes resultedexclusively in R-configured alkanes and S-configuration for carbocyclicalkenes (A. Pfaltz, F. Menges, Adv. Synth. Catal. 2002, 344/1, pp.40-44, A. Pfaltz et al. Adv. Synth. Catal. 2003, 345/1-2, pp 33-43). Noliterature data were found for successful enantioselective hydrogenationof heterocyclic alkenes. In the synthesis using heterocyclic alkenes,the stereospecificity (as either S configuration or R configuration) ofthe substituted carbon of the synthesized heterocyclic alkane compoundcan either conform with, or oppose, the stereospecificity of thecatalyst ligand. In one embodiment of the present invention, the use ofthe (4S,5S)-phospine-oxazoline ligand in the synthesis using afunctionalized heterocyclic alkene (the dehydroequol compound (VII))resulted exclusively in the R-configured chromane (R-equol), while theuse of the (4R,5R)-phosphine-oxazoline ligand resulted exclusively in anS-configured chromane (S-equol).

There is some indication, referred to in Example 9, that thehydrogenation of the 3-phenyl-3,4-chromene forms a corresponding2,3-chromene intermediate, which then is hydrogenated to the chromane.In such case, the 3-phenyl-2,3-chromene may be a novel, isolatedcompound, and can be an alternative starting chromene for theenantioselective hydrogenation method of the present invention.

The synthesized enantiomer of equol can be converted into an equolanalog or conjugate at the C-4′ or the C-7 position with a conjugateselected from the group consisting of glucuronide, sulfate, acetate,propionate, glucoside, acetyl-glucoside, malonyl-glucoside, and mixturesthereof.

The resulting enantiomeric equol material typically has an enantiomericexcess (ee) of at least 10%, more typically at least 50%, more typicallyat least 90%, and even more typically of at least 95%, and typically upto 100%, more typically up to 99.5%, and more typically up to 99%.

An alternative starting material for the synthesis of equol is achromen-4-one, such as a 3-phenyl-chromen-4-one, which is availablenaturally and commercially as daidzein or its methoxy analog,formononetin. Daidzein can be synthesized by known methods, such as thatdescribed in J. Chem. Soc. Perkin Trans., 1991, pages 3005-3008,incorporated herein by reference. The starting daidzein can be protected(for example, with a protecting group PG, such as MOM). In a preferredsynthesis route, purified bis-MOM daidzein, shown below as compound(XI), is hydrogenated to obtain a cis- and trans-mixture (1:1) of thecorresponding 3-phenyl-chroman-4-one, shown as compound (XII):

A 10% Pd/C catalyst and NH₄CO₂H in methanol solvent was found suitableto convert the daidzein to the racemic chroman-4-one overnight at roomtemperature. The isolated 3-phenyl-chroman-4-one product is then reducedto a corresponding cis- and trans-mixture (about 3.4:1) of bis-MOMdaidzein-ol (compound (XIII)) according to the reaction:

The bis-MOM daidzein-ol (a chromen-ol) is then dehydrated to introducethe double bond within the heterocylic ring, between the ring carbons inthe 3 and 4 positions, resulting in formation of the 3,4-dehydroequol(compound (XIV)), according to the reaction:

The 3,4-dehydroequol can be purified by crystallization to form a whitesolid (powder), which can be stabilized by storage in solid form in afreezer. The presence of air, moisture and storage in solvent for anextended time may cause decomposition of the dehydroequol.

A preferred Ir catalyst system comprises and IR-ligand complex (complex(XV)), comprised of the ligand shown as compound (V), with Ir and((COD)Cl)2.

An Ir-ligand complex can be obtained by refluxing thephosphine-oxazoline ligand with [Ir(COD)Cl]₂ in dichloromethane understandard conditions for about 1 hour. The Ir-ligand complex is thenreacted with a counterion in aqueous dichloromethane to form the chiralIr catalyst system as described by A. Pfaltz in Adv. Synth. Catal. 2002,344/1, pp 40-44. A preferred iridium catalyst ligand comprises thephosphine-oxazoline ligand compound (IX) shown herein before. Apreferred counterion is NaB(Ar_(f))₄, shown as compound (XVI):

A functional group or substituent, such as a hydroxyl, sulfhydryl, oramino group, is termed “protected” when the substituent is modified topreclude undesired side reactions at the protected site. Suitableprotecting groups for the compounds of the present invention will berecognized from the present application taking into account the level ofskill in the art, and with reference to standard textbooks, such asGreene et al., Protective Groups in Organic Synthesis (New York: Wiley,1991).

Non-limiting examples of hydroxyl-protecting groups useful in thisembodiment include, without limitation: alkyl, typically methyl, ethyl,tert-butyl and benzyl; alkoxy alkyl, typically methoxy methyl (“MOM”),benzyloxy methyl, p-methoxy benzyl, and dimethoxy benzyl; silylmoieties, including trialkylsilyl such as triisopropylsilyl (“TIPS”) andtrimethylsilyl (“TMS”) moieties; acyl moieties, such as acetyl andbenzoyl; tetrahydropyranyl and related moieties; methylthiomethyl; andsulfonyl moieties, such as methane sulfonyl and benzene sulfonyl.

The protecting groups may be removed using conventional reagents andmethods to give the unprotected chromane or chromene.

Use of Enantiomeric Equol

The synthesized stereoselective, enantiomeric equol compounds, S-equoland R-equol, can be used as the isolated enantiomer, or in a racemic(1:1) or non-racemic mixture, to make commercial and institutionalproducts. The enantiomeric equol, or a composition or product madetherefrom, can be consumed orally or applied topically, intradermally,subcutaneously, or inhaled in carrier, and can comprise a marketed orinstitutional food product, a pharmaceutical, an OTC medicament, anointment, liquid cream or other material suitable for topicalapplication. A typical food composition can comprise at least 1 mg, andup to 200 mg, of the enantiomer of equol per serving. Anorally-administered medicament can comprise at least 1 mg, and up to 200mg, of the enantiomer of equol per dose. A product for topicalapplication can comprise at least 0.1%, and up to 10%, by weight of theenantiomer of equol.

Enantiomeric equol, or a composition or preparation made therefrom, canbe administered to subjects for the treatment and/or prevention of, orfor reducing the predisposition to, diseases and conditions relatedthereto. Compositions or products can also include one or morepharmaceutically acceptable adjuvants, carriers and/or excipients. Othercompositions and products that can be made from enantiomeric equol, andtheir uses in the treatment or prevention of diseases and conditions,are disclosed in PCT Publication WO 2004/23056, published Jan. 29, 2004,and in PCT Publication WO 2004/039327, published May 13, 2004,incorporated herein by reference.

METHODS A. Method for Synthesizing (4R,5R)-phosphine-oxazoline Ligand

The (4R,5R)-phosphine-oxazoline ligand, shown herein before as compound(X), was synthesized substantially in accordance with Examples A12 andB12 of U.S. Pat. No. 6,632,954, issued to Pfaltz et al, and incorporatedherein by reference. Whereas Pfaltz started out with L-threonine andproduced the (4S,5S)-phosphine-oxazoline, this method starts out withD-threonine.

a) Preparation of D-Threonine methyl ester

A solution of gaseous HCl in methyl alcohol (210 mL of 2N, or 0.46 mol)was placed in a 0.5 L 3 neck round bottom flask equipped with a magneticstirrer, thermocouple, nitrogen line, condenser and heating mantle. Atotal of 25.1 g (0.21 mol) of D-threonine (98%, Aldrich) was added tothe HCl/MeOH solution at room temperature and resulted mixture wasrefluxed overnight. The reaction was monitored by TLC usingEtOAc/MeOH/AcOH=7:2.5:0.5 mixture as a mobile phase. The reaction wasstopped when all D-threonine was essentially consumed (R_(f)=0.32 forD-threonine methyl ester, gives a “carrot”-hued spot with ninhydrin, andR_(f)=0.19 for D-threonine—a red spot with ninhydrin). A solvent wasremoved on rotavap to yield 39.49 g (110% yield) of a glass-lookingmaterial, which was used in the next step without purification.

b) Preparation of N-benzoyl-d-threonine methyl ester

A crude D-threonine methyl ester (39.49 g) was dissolved in 300 mL ofmethanol and than transferred to the 1 L 3-neck round bottom flaskequipped with a thermocouple, magnetic stirrer and cooling ice bath. Asolution was chilled to 12° C., and a total of 64.1 g (0.63 mol, 3 eq.)was added to the flask and then cooled to −10° C. A total of 30.9 g(0.21 mol) of benzoyl chloride was added to the solution and resultingmixture stirred at 0° C. for 1 hour. After this period of time thesolvent was removed on rotovap to yield a viscous semi-solid. A total of300 mL of cold water was added to the residue and organic material wasextracted with ethyl acetate (2×300 mL). The organic phase wasseparated, washed with brine (200 mL) and dried over sodium sulfate. Thesolvent was removed on rotovap to yield 52.02 g (104%) of a clear yellowoil with Rf=0.39 in EtOAc/hexane=6:4). Obtained oil was crystallizedfrom 200 mL of ether to give a white solid, which was filtered off,washed with hexane (2×100 mL) and dried under suction. An additionaldrying in a vacuum desiccator yielded 42.35 g (84.7% yield in 2 steps).

¹H-NMR (300 MHz, CDCl₃, δ): 1.25 (d, j=6.3 Hz, 3H, CH₃), 3.42 (d, 1H,OH), 3.78 (s, 3H, OCH₃), 4.42 (dq, J=2.6 Hz, J=6.3 Hz, 1H, CH—O), 4.78(dd, J=2.4 Hz, J=8.7 Hz, 1H, CH—N), 7.2 (bd, J=9.0 Hz, 1H, NH), 7.40 (t,J=7.3 Hz, 2H, Ph), 7.43 (t, J=7.3 Hz, 1H, Ph), 7.82 (d, J=7.3 Hz, 2H,Ph). ¹³C APT NMR (75 MHz, CDCl3, δ): 19.94, 52.47, 57.79, 67.97, 127.14,128.48, 131.80, 133.56, 168.07, 171.49.

c) Preparation of(4R,5R,)-5-methyl-2-phenyl-4,5-dihydrooxazole-4-carboxylic acid methylester

An excess of thionyl chloride (75 mL) was placed in a 250 mL roundbottom flask equipped with a thermocouple, magnetic stirrer, causticscrubber and cooling dry ice/acetone bath and was cooled to −35° C. Asolid N-benzoyl-D-threonine methyl ester (25.75 g, 0.108 mol) was addedportion-wise to the flask while maintaining reaction temperature at −20°C. After completed addition, the resulting mixture was slowly warm up toroom temperature and stirred for additional 1 hour. The reaction waskept overnight at ˜5° C. after that an excess of thionyl chloride wasremoved under vacuum at ˜30° C. Obtained oil was washed with saturatedcold sodium bicarbonate (1.5 L), extracted with dichloromethane (3×200mL) and the organic phase was dried over sodium sulfate. The solvent wasremoved on rotovap to yield 22.93 g of clear oil. This oil was purify on13×9 cm silica gel plug using CH₂Cl₂/hexane=1:1 as eluent to give 19.88g (83.6% yield) of clear oil which slowly crystallized to while solid(R_(f)=0.17 in CH₂Cl₂/hexane=1:1).

¹H-NMR (300 MHz, CDCl₃, δ): 1.40 (d, J=6.3 Hz, 3H, CH₃), 3.80 (s, 3H,OCH₃), 4.97 (d, J=10.2 Hz, 1H, CH—N═C), 5.05 (J=6.0 Hz, J=10.2 Hz, 1H,CH—O), 7.41 (t, J=7.5 Hz, 2H, Ph), 7.50 (t, J=7.3 Hz, 1H, Ph), 7.43 (t,J=7.3 Hz, 1H, Ph), 8.00 (d, J=7.3 Hz, 2H, Ph). ¹³C NMR (75 MHz, CDCl3,δ): 16.13, 51.96, 71.67, 77.55, 127.17, 128.21, 128.44, 131.69, 166.06,170.31.

d) Preparation of(4R,5R)-2-(5-Methyl-2-phenyl-4,5-dihydrooxazol-4-yl)-1,3-diphenyl-propan-2-ol

A solution of 8.61 g (39.27 mmol) of(4R,5R,)-5-methyl-2-phenyl-4,5-dihydrooxazole-4-carboxylic acid methylester in 200 mL of anhydrous diethyl ether was placed in a 200 mL threeneck round bottom flask equipped with a thermocouple, nitrogen line,magnetic stirrer and cooling dry ice/acetone bath. A total of 120 mL(120 mmol, 3 eq.) of 1M solution of benzylmagnesium chloride in diethylether was added to the reaction at −78° C. via syringe. The cooling bathwas removed, and the reaction mixture was allowed to warm up to roomtemperature whiting 2 hours and stirred for one hour at thistemperature. Resulted milky solution was poured on cold aqueous solutionof ammonium chloride (1.2 L) and extracted with ethyl acetate (2×200mL). The organic layer was washed with water (200 mL) and brine (100mL). After drying over sodium sulfate the solvent was evaporated underreduced pressure to afford 16.95 g of clear oil. The crude product waspurified on silica gel column using hexane/ethyl acetate=25/1 mixture aseluent to yield 13.75 g (86% yield) of pure material as a whitefoam/powder with R_(f)=0.49 in EtOAc/hexane=1:9.

¹H-NMR (300 MHz, CDCl₃, δ): 1.70 (d, J=6.6 Hz, 3H, CH₃), 2.10 (s, 1H,OH), 2.67 (d, J=13.8 Hz, 1H, CH₂), 2.92 (J=13.8 Hz, 1H, CH₂), 3.11 (d,J=14.1 Hz, 1H, CH₂ 3.17 (d, J=13.8 Hz, 1H, CH₂), 4.10 (d, J=9.3 Hz, 1H,CH—N═C), 4.81 (dq, J=6.9 Hz, J=9.3 Hz, 1H, CH—O), 7.20-7.30 (m, 13H,Ph), 8.05 (d, J=7.3 Hz, 2H, Ph). ¹³C NMR (75 MHz, CDCl₃, δ): 16.70,42.22, 42.75, 71.81, 76.13, 79.34, 126.42, 128.08, 128.10, 128.23,130.95, 131.31, 137.11, 137.22, 164.06.

e) Preparation of(4R,5R)-O-[1-Benzyl-1-(5-methyl-2-phenyl-4,5-dihydrooxazol-4-yl)-2-phenylethyl]-diphenyl-phosphinite

A solution of 6.64 g (16.44 mmol) of(4R,5R)-2-(5-Methyl-2-phenyl-4,5-dihydrooxazol-4-yl)-1,3-diphenyl-propan-2-olin 200 mL of anhydrous pentane was placed in a 500 mL three neck roundbottom flask equipped with thermocouple, nitrogen line, magnetic stirrerand cooling dry ice/acetone bath.

A total of 13 mL (20.8 mmol, 1.26 eq.) of 1.6M solution of n-butyllithium in hexane was added to flask at −78° C. followed by addition of4.32 g (37.17 mmol, 2.26 eq.) N,N,N′,N′-tetramethylethylenediamine. Thecooling bath was removed and the mixture was warmed up to 0° C. whiting1 hour and stirred an additional 1.5 hour. After this period of time, atotal of 4.10 g (18.58 mmol) of diphenylchlorophosphine was added to thereaction, and resulting mixture was allowed to warm up to roomtemperature. After stirring at this temperature for 3 hours, the solventwas removed on rotovap and off-while semisolid was obtained. The crudeproduct was dissolved in minimal amount of dichloromethane and thenpurified via silica gel plug using EtOAc/hexane=1:20 as an eluent toyield 8.78 g (96% yield) of white foam with Rf=0.56 in EtOAc/hexane=1:9.The isolated foam was purified one more time using silica gel column andEtOAc/hexane=1:50 to give 5.56 g (61% yield) of pure product as a bulkywhite powder.

f) Preparation of Sodium tetrakis[3,5-bis-(trifluoromethyl)-phenyl]-borate (as described by D. L. Reger,T. D. Wright, C. A. Little, J. J. S. Lamba, M. D. Smith in Inorg. Chem.,2001, 40, 3810-3814)

Step f-1: A total of 3.49 g (31.7 mmol, 1 eq.) of sodiumtetrafluoroborate, 4.98 g (205 mmol, 6.45 eq.) and 600 mL of anhydrousether were charged in a 2 L 4 neck round bottom flask, equipped withoverhead stirrer, addition funnel, thermocouple, condenser, nitrogenline and heating mantle. Dibromoethane (˜1 mL) was added, and the flaskwas gently heated to initiate the reaction. The heat was removed, and asolution of 50.94 g (174 mmol, 5.47 eq.) of3,5-bis-(trifluoromethyl)-bromobenzene in 100 mL of ether was addeddropwise within 30 min, which caused the solution to gently reflux. Onceall bromide was added, the reaction was heated with a heating mantle tocontinue the reflux for an additional 1 hour. The heat than was removed,and the resulted mixture stirred overnight at room temperature. Afterthis period of time, the reaction mixture was poured on a cold solutionof sodium carbonate (77 g of Na₂CO₃ in 950 mL of water) and stirred for30 min. The top brown organic layer was separated, and the bottom milkyaqueous layer was extracted with ether (2×300 mL). Combined organicphases were dried over sodium sulfate and stirred with 17 g of charcoalfor 2 hours at room temperature. The mixture was filtered through theCelite pad, and the ether was removed on a rotovap to yield 32.4 g ofbrown semisolid. The obtained crude product was dissolved in 300 mL ofbenzene and water was removed with a Dean-Stark trap by azeotropicdistillation for 3 hours. The solvent volume was reduced to about 200 mLand the residue was cooled on an ice bath to form a mixture of a solidand heavy brown oil. The heterogeneous mixture was filtered off, washedwith benzene (3×50 mL) followed by hexane wash (1×100 mL). The isolatedsolid was dried under suction and nitrogen flow to yield 13.28 (47%yield) of white solid with R_(f)=0.15 in EtOAc.

Step f-2: Chiral (4R,5R)-Iridium Complex; (by analogy with the synthesisof 4S,5S-iridium complex described by A. Pfaltz in Adv. Synth. Catal.2002, 344/1, pp 40-44). A solution of 5.49 g (9.88 mmol, 1.82 eq.) of(4R,5R)-O-[1-Benzyl-1-(5-methyl-2-phenyl-4,5-dihydrooxazol-4-yl)-2-phenylethyl]-diphenyl-phosphinitein 150 mL dichloromethane was placed in a 500 mL three neck round bottomflask equipped with a thermocouple, magnetic stirrer, condenser,nitrogen line and a heating mantle. A total of 3.65 g (5.43 mmol, 1 eq.)of the iridium complex [Ir(COD)Cl]₂ was added portion-wise to the flaskand formed red solution was refluxed for 2 hours. The heating mantle wasremoved, and 10.25 g (11.56 mmol, 1.17 eq.) of solid sodiumtetrakis[3,5-bis-(trifluoromethyl)-phenyl]-borate was added to thereaction mixture. The resulted mixture vigorously stirred for 5 min andafter that was diluted with 130 mL of water. The heterogeneous mixturestirred for an additional 15 min and the layers were separated. Theaqueous phase extracted with dichloromethane (2×100 mL) and combinedorganic layers dried over sodium sulfate. The solvent was evaporatedunder reduced pressure to afford 19.05 g of orange foam. The obtainedcrude material was purified via silica gel plug (366 g of SiO₂) usingCH₂Cl₂/hexane=1:1 as an eluent. The solvent was removed on rotovap togive 14.81 g (79% yield) of the catalyst as a bright orange powder withR_(f)=0.28 in CH₂Cl₂/hexane=6:4.

B. Method for TMS and TBDMS Derivitization

a. TMS: 20 μg of R-Equol and S-Equol were placed into separatederivitization vials and dried down under nitrogen. Six drops of Tri-SilReagent were added to each vial using a glass pipet, and the contentsheated for 30 minutes at 65° C. The treated sample was dried undernitrogen and reconstituted in 50 μL of hexane. The sample was then runvia GC/MS.

b. TBDMS: 20 μg of R-Equol and S-Equol were placed into separatederivitization vials and dried down under nitrogen. An amount of 100 μLof Acetonitrile and 100 μL of MTBSTFA+1% t-BDMCS were added to eachvial, and the contents heated for 1 hour at 100° C. The treated samplewas dried under nitrogen and reconstituted in 50 μL of hexane. Thesample was then run via GC/MS.

C. GC/MS and LC/MS Analysis

GCMS: Products and intermediate products were analyzed using a VGAutospec magnetic sector mass spectrometer equipped with an HP GasChromatograph 5890 series II. A solid glass needle injector was used toinject samples onto a J&W Scientific DB1 column, 0.25 mm I.D., 0.25 μmfilm using helium as the carrier gas. A temperature gradient starting at225° C. for 1.0 min, then ramped to 310° C. and held for 10 min was usedbefore making the next injection. The EI+ magnetic scan experiment wasused to acquire fullscan traces and spectrum of all products with a massrange of 100-900.

LCMS: Products and intermediate products were analyzed using a WaterQuattro Micro API tandem mass spectrometer equipped with a WatersAcquity UPLC. The two mobile phase system using water, 2 mM ammoniumacetate (mobile phase A) and methanol, 2 mM ammonium acetate (mobilephase B) with 0.1% formic acid was held isocratic at 50/50. A rheodyneinjector was plumbed immediately before the probe, allowing for directloop injections into the instrument. The MS experiment with capillarypotential 3.5 kV, cone 18V, a collision gas of 18, mass range 100-500,under ESI+ was created to acquire the fullscan traces and spectrum ofall products.

EXAMPLES Example 1 Synthesis of the MOM-protected chromen-one (bis-MOMDaidzein,7-methoxymethoxy-3-(4′-methoxymethoxy-phenyl)-2H-chromen-4-one)

A total of 329 g (1.29 mol) of 97% daidzein (from LLC Laboratories) wasmixed with 4.5 L of dichloromethane in a 12 L 4-neck round bottom flaskequipped with a thermocouple, overhead stirrer, heating mantle, additionfunnel and nitrogen line. The resulted white suspension was chilled to8° C., and a total of 655.8 g (6.07 mol, 3.9 eq.) ofdiisopropylethylamine (DIEA) was added to the pot. After 20 min a totalof 373 g (4.63 mol, 3.59 eq.) of chloromethylmethyl ether (MOM-Cl) wasadded to the mixture via an addition funnel at 8° C. An ice bath wasremoved, replaced with a heating mantle and allowed to warm up to roomtemperature within 2 hours. The pot temperature was maintained at 40° C.and reaction was kept (usually overnight) at this temperature untildaidzein and mono-MOM intermediate disappeared according to TLC(R_(f)=0.23 for daidzein, 0.38 for mono-MOM and 0.62 forbis-MOM-daidzein in EtOAc/hexane=1.1). The resulted clear brown solutionwas cooled to room temperature, and slowly poured under agitation on acold mixture of 4 L of water, 1 kg of ice, 1 L of saturated sodiumbicarbonate and 3 L of dichloromethane, which was prepared in a 20 Lplastic bucket equipped with a powerful overhead stirrer andthermocouple. The pH of the resulted solution must stay basic duringthis work up to avoid degradation of the product. The organic phase wasseparated, and aqueous was back extracted with dichloromethane (2×1 L).The organic layers were combined, washed with water (2×3 L), sodiumbicarbonate (3 L) and dried over sodium sulfate (500 g). The solvent wasremoved under reduced pressure to give 431 g (97% yield) of the productas a yellow solid. This material was purified by crystallization from3.5 L of hot (56° C.) ethyl acetate followed by filtration andconsequent washes with EtOAc/hexane=3:1 (2 L). Separated solid was driedovernight at 35° C. in a vacuum oven to yield 340.6 g (77% isolatedyield) of bis-MOM-daidzein as a white solid. A second crop (a total of66.31 g of the product) was isolated from a mother liquor to give abis-MOM-daidzein in the 91.78% combined yield.

Gas Chromatography Mass Spectrometry (GC-MS) traces and spectra wereobtained on the bis-MOM Daidzein product according to the GC-MS Methoddescribed in the Methods Section, and are shown in FIGS. 1A and 1B,respectively. Liquid Chromatography Mass Spectrometry (LC-MS) traces andspectra were obtained on the bis-MOM Daidzein product according to theLC-MS Method described in the Methods Section, and are shown in FIGS. 1Cand 1D, respectively.

¹H NMR and ¹³C NMR data appear below.

¹H NMR (300 MHz, CDCl₃, δ): 8.21 (d, 1H, J=9.3 Hz), 7.92 (s, 1H), 7.48(d, 2H, J=9.0 Hz), 7.07 (m, 4H), 5.26 (s, 2H, OCH₂O), 5.20 (s, 2H,CH₂O), 3.50 (s, 3H, CH₃O), 3.48 (s, 3H, CH₃O). ¹³C NMR (75 MHz, CDCl₃,δ): 175.697, 161.337, 157.543, 152.228, 130.045, 127.716, 125.329,124.690, 119.076, 116.147, 115.370, 102.969, 94.280, 56.290, 55.861.

Example 2 Hydrogenating the chromen-one to a chroman-one(7-methoxymethoxy-3-(4′-methoxymethoxy-phenyl)chroman-4-one)

A total of 336.5 g (0.983 mol) of bis-MOM-daidzein and 3.3 L of methanolwere charged in a 12 L 4-neck round bottom flask equipped with acondenser, thermocouple, overhead stirrer, heating mantle and nitrogenline. A solid ammonium formate (309.4 g, 4.906 mol, 5 eq.) was added tothe flask under agitation and a resulting slurry stirred for 20 min atroom temperature. A total of 23.2 g (6.89 wt %) of dry 10% Pd/C wascarefully transferred to the pot under nitrogen atmosphere and thereaction temperature was maintained at 45° C. The reaction was monitoredby TLC (R_(f)=0.22 for bis-MOM-daidzein and 0.29 for the product inEtOAc/hexane=2:8) until all starting material disappeared (usually itrequires 5 hours). Warm (˜30° C.) reaction mixture was filtered throughCelite (142 g) in order to remove the catalyst, and the filter waswashed with 2 L of dichlorometane. Organic filtrates were combined, andthe solvent was removed under reduced pressure to give a yellow solid,which was recrystallized from methanol-hexane to yield 241.2 g (71.3%yield) of the product as a white solid. An additional amount (36.94 g)was isolated from a mother liquor to give the product in 82.2% combinedyield.

GC-MS traces and spectra of the chroman-4-one product are shown in FIGS.2A and 2B, respectively. LC-MS traces and spectra of the chroman-4-oneproduct are shown in FIGS. 2C and 2D, respectively.

¹H NMR and ¹³C NMR data appear below.

¹H NMR (300 MHz, CDCl₃, δ): 9.0 (d, 1H, J=9.0 Hz), 7.95 (dd, 2H, J=9.0Hz, J=2.4 Hz), 7.00 (dd, 2H, J=9.0 Hz, J=2.4 Hz), 6.70 (dd, 1H, J=8.7Hz, J=2.1 Hz), 6.62 (d, 1H, J=2.4 Hz), 5.20 (s, 2H, OCH₂O), 5.15 (s, 2H,OCH₂O), 4.62 (d, 1H, CH₂O, J=0.6 Hz), 4.60 (d, 1H, CH₂O, J=2.7 Hz), 3.87(dd, 1H, CH, J=7.8 Hz, J=6.0 Hz), 3.47 (s, 3H, CH₃O), 3.45 (s, 3H,(CH₃O). ¹³C NMR (75 MHz, CDCl₃, δ): 190.98, 163.441, 163.174, 156.686,129.560, 129.423, 128.516, 94.312, 94.029, 71.782, 56.290, 55.853,51.145.

Example 3 Reducing the chroman-one to a chroman-ol(7-methoxymethoxy-3-(4′-methoxymethoxy-phenyl)chroman-4-ol) as a mixtureof cis- and trans-isomers

A total of 25.33 g (0.67 mol) of solid sodium borohydride was charged ina 12 L 4-neck round bottom flask equipped with a thermocouple, overheadstirrer, cooling ice/methanol bath, addition funnel and nitrogen line. Atotal of 3 L of dry THF was added to the flask and resultant suspensionwas cooled to 1.4° C. The glacial acetic acid (52.54 g, 0.875 mol) wasslowly added to the flask as a solution in 200 mL of THF, and themixture stirred at 10° C. for 20 min. The reaction was cooled to −4° C.and a solution of 230.1 g (0.668 mol) of bis-chroman-4-one in 1.3 L ofTHF was added to the flask. The reaction slowly agitated for three daysat room temperature and monitored by TLC until all starting ketonedisappeared. The reaction was quenched by addition to 12 L of coldsaturated solution of ammonium chloride, organic layer was separated,and aqueous phase was extracted with dichloromethane (2×1 L). Combinedorganic phases washed with water (1×3 L) and dried over sodium sulfate.Solvent was removed under reduced pressure to yield 229.7 g (99.2%yield) of the product as a colorless viscous oil (as a mixture ofcis-trans=3:1 isomers). This material was used in next step without anypurification.

GC-MS traces and spectra of the chroman-ol product are shown in FIGS. 3Aand 3B, respectively. LC-MS traces and spectra of the chroman-ol productare shown in FIGS. 3C and 3D, respectively. Each mass spec analysisprovided a MW for the chroman-ol product as 328, whereas the actual MWof 346, a difference of 18. Since the NMR data confirm the structure ofthe product, it is believed that the chroman-ol product may havedehydrated during the ionization of the sample during the mass specanalyses, resulting in a loss of one water molecule, which caused thecharged molecular ion in the mass spectrometric analysis to appear 18a.m.u. lower in mass.

¹H NMR and ¹³C NMR data appear below.

¹H NMR (300 MHz, CDCl₃, δ, trans-isomer): 7.32 (d, 1H, J=8.7 Hz), 7.12(dd, 2H, J=8.7 Hz, J=2.1 Hz), 6.98 (dd, 2H, J=8.4 Hz, J=1.8 Hz), 6.63(dd, 1H, J=8.4 Hz, J=2.7 Hz), 6.54 (d, 1H, J=2.4 Hz), 5.12 (s, 4H,OCH₂O), 4.81 (dd, 1H, CHOH, J=7.5 Hz, J=5.1 Hz), 4.30 (dd, 1H, CH₂O,J=10.8 Hz, J=3.3 Hz), 4.18 (dd, 1H, CH₂O, J=11.4 Hz, J=8.4 Hz), 3.44 (s,6H, CH₃O), 3.04 (ddd, 1H, CH, J=11.4 Hz, J=8.3 Hz, J=3.3 Hz), 2.27 (d,1H, OH). For cis-isomer: 7.20-7.10 (m, 3H), 7.05-6.95 (m, 2H), 6.68-6.52(m, 2H), 5.14 (s, 2H, OCH2O), 5.13 (s, 2H, OCH2O), 4.68 (br.s, 1H), 4.51(dd, 1H, J=12.0 Hz, J=10.5 Hz), 4.3-4.1 (m, 1H), 3.45 (s, 6H, CH₃O),3.23 (ddd, 1H, J=11.7 Hz, J=6.6 Hz, J=3.3 Hz. ¹³C NMR (75 MHz, CDCl₃, δtrans-isomer): 157.964, 156.443, 131.971, 129.366, 129.204, 128.921,118.331, 116.608, 109.489, 109.327, 103.810, 94.337, 94.304, 69.023,68.069, 55.910, 55.877, 46.186.

Example 4 Dehydration of the chroman-ol to the chromenebis-MOM-dehydroequol (7-methoxymethoxy-3-(4′-methoxymethoxy-phenyl)-2H-chromen)

A solution of 227.7 g (0.658 mol) of the above alcohol (as a mixture ofcis-trans isomers) was dissolved in 3.5 L of THF and transferred in a 12L 4-neck round bottom flask equipped with a thermocouple, overheadstirrer, cooling ice/methanol bath, addition funnel and nitrogen line. Atotal of 667.3 g (6.58 mol) of Et₃N was added to the alcohol solution at−8° C. followed by addition of 222.7 g (1.28 mol) of methanesulfonicacid anhydride in 1.5 L of THF. The reaction was allowed to warm up toroom temperature while monitoring by HPLC and stirred until all alcoholdisappeared (about 2 hours). The reaction was quenched by addition tothe 10 L of cold water. The organic layer was separated, and the aqueousphase extracted with dichloromethane (2×2 L). Combined organic layerswere washed with water (2×3 L) and dried over sodium sulfate. Solventwas removed under reduced pressure to form a viscous semisolid material.The resulted mixture was diluted with hexane (1.5 L) and cooled on anice. Precipitated solid was filtered off, washed with hexane (2×1 L) anddried under nitrogen to give 136 g (63% yield) of bis-MOM-dehydroequolas a white solid. Additional 10 g was isolated from mother liquor togive a total of 146 g of the product in 69% combined yield. Isolatedalkene (131.6 g) was additionally purified on silica gel plug usingdichloromethane as an eluent to yield 124.8 g (94.8% recover) ofbis-MOM-dehydroequol as a white solid. This material was used forasymmetric hydrogenation.

GC-MS traces and spectra of the bis-MOM-dehydroequol product are shownin FIGS. 4A and 4B, respectively. LC-MS traces and spectra of thebis-MOM-dehydroequol product are shown in FIGS. 4C and 4D, respectively.

¹H NMR and ¹³C NMR data appear below.

¹H NMR (300 MHz, CDCl₃, δ): 7.33 (dd, 2H, J=8.7 Hz, J=2.1 Hz), 7.03 (dd,2H, J=8.7 Hz, J=1.8 Hz), 6.97 (d, 1H, J=9.0 Hz), 6.67 (s, 1H, HC═C),5.59 (dd, 2H, J=7.2 Hz, J=2.4 Hz), 5.17 (s, 2H, OCH₂O), 5.14 (s, 2H,OCH₂O), 5.09 (d, 2H, OCH₂C═C, J=1.2 Hz), 3.46 (s, 6H, CH₃O). ¹³C NMR (75MHz, CDCl₃, δ); 157.883 (C7), 156.855 (C9), 154.153 (C4′), 130.596(C10), 128.816 (C3), 127.360 (C8), 125.750 (C6), 118.323 (C4), 117.401(C1′), 116.390 (C3′), 109.319 (C5), 103.842 (C2′), 94.377 (OCH₂O),94.329 (OCH₂O), 67.171 (C2), 55.958 (CH₃O).

Example 5 Enantioselective hydrogenation of bis-MOM dehydro-equol toMOM-protected S-equol((S)-7-(methoxymethoxy)-3-(4′-methoxymethoxy)-phenyl chroman)

A solution of 60.48 g (0.184 mol) of bis-MOM-dehydroequol and 3.10 g(0.0018 mol, 1 mol %) of((4R,5R)-(−)-O-[1-Benzyl-1-(5-methyl-2-phenyl-4,5-dihydro-oxazol-4-yl)-2-phenylethyl]-diphenylphosphinite-(1,5-COD)-iridium(I)tetrakis-(3,5-bis-trifluoromethyl)-phenylboratein 1.3 L of dichloromethane was placed in a 2 L glass reactor equippedwith a magnetic stirrer, thermocouple, gas inlet tube and a pressurerelief valve. The air was replaced with nitrogen followed by hydrogenpurge, and a 60 psig hydrogen pressure was maintained. The reactionmixture was monitored with TLC (R_(f)=0.26 for startingbis-MOM-dehydroequol, greenish spot with PMA on hot plate, andR_(f)=0.28 for bis-MOM-equol, a purple spot with PMA, in ethylacetate/hexane=1:9). The reaction can be monitored by GC-MS (HP 5890 andMS 5972 were used, column DB-5MS, 30 m length, 0.25 mm ID, 0.25 μm film,He carrier gas, flow rate 1.7 mL/min. Temp. program: 50° C. for 1 min,20° C./min to 300° C., hold at 300° C. for 5 min, run time is 18.5 min.Retention time for the product is 15.77 min, and 16.41 min for thestarting material).

The reaction was kept at 60 psig hydrogen pressure for 110 min until allstarting material is consumed. Hydrogen was immediately replaced withnitrogen and clear red solution was quenched with a cold ammoniumchloride solution (1 L of saturated ammonium chloride and 2 kg of ice).The organics were extracted with dichloromethane (2×1 L), combinedorganic phases were washed with 2 L of water and dried over sodiumsulfate. Solvent was removed on rotavap and a red oil was purified onsilica gel using ethyl acetate/hexane=2:8 mixture as an eluent to yield42.8 g (7.3% yield) of bis-MOM-equol as a white solid with mp 37-38° C.

GC-MS traces and spectra of the MOM-protected S-equol product are shownin FIGS. 5A and 5B, respectively. LC-MS traces and spectra of theMOM-protected S-equol product are shown in FIGS. 5C and 5D,respectively.

¹H and NMR and ¹³C NMR data appear below.

¹H NMR (300 MHz, CDCl₃, δ): 7.16 (d, 2H, J=8.7 Hz), 7.02 (d, 2H, J=8.7Hz), 6.9 (s, 1H), 6.59 (dd, 1H, J=9.0 Hz, J=2.4 Hz), 6.58 (s, 1H), 5.17(s, 2H, CH₂O) 5.14 (s, 2H, CH₂O), 4.30 (ddd, 1H, J=10.8 Hz, J=4.2 Hz,J=1.5 Hz), 3.96 (t, 1H, J=10.8 Hz), 3.47 (s, 6H, CH₃O), 3.17 (m, 1H,CH), 2.93 (d, 2H, J=8.7 Hz, CH₂). ¹³C NMR (75 Mhz, CDCl3, δ): 156.653(C7), 156.265 (C9), 154.938 (C4′), 134.681 (C10), 130.151 (C8), 128.330(C6), 116.576 (C3′), 115.532 (C1′), 109.020 (C5), 104.344 (C2′), 94.571(OCH₂O), 94.498 (OCH₂O), 71.022 (C2), 55.950 (CH₃O), 55.918 (CH₃O),37.893 (C3), 31.891 (C4).

Example 6 Deprotecting the bis-MOM-S-equol to S-Equol((S)-3-(4-hydroxyphenyl)-chroman-7-ol)

A solution of 42.17 g (0.128 mol) of (S)-bis-MOM-equol in 200 mL of 1:1mixture of CH₂Cl₂/MeOH was placed in a 1 L 3-neck round bottom flaskequipped with a magnetic stirrer, thermocouple, cooling ice bath andnitrogen line. A total of 200 mL of 10 wt % solution of HCl in MeOH(0.438 mol, 3.4 eq.) was slowly added to pre-chilled (4.8° C.) solutionof bis-MOM-equol. The reaction mixture was allowed to warm up to roomtemperature and monitored by TLC until all starting material isconverted to S-equol (R_(f)=0.58 for bis-MOM-equol, 0.28 formono-MOM-equol, and 0.10 for S-equol in ethyl acetate/hexane=2:8). After6 hours at room temperature a complete deprotection was observed.Solvent was removed under reduced pressure and precipitated solid wastreated with a 500 mL of ice-cold water, extracted with ethyl acetate(2×400 mL) and combined organic phases were washed with diluted sodiumbicarbonate (400 mL). Organic layer was dried over sodium sulfate andsolvent volume was reduced to about 100 mL. The obtained yellowishsolution was carefully diluted with 400 mL of hexane and resulted clearsolution was chilled on an ice bath while stirring. Precipitated whitesolid was filtered off, washed with hexane (3×200 mL) and dried in avacuum oven overnight to yield 25.24 g of s-equol as a white solid. Anadditional 3.54 g of the product was obtained from mother liquor. Atotal 28.78 g (93% isolated yield) of S-equol was obtained as a whitesolid with mp 162° C. Chemical HPLC and optical purity for synthesizedS-equol were found to be 96.69% and 100% ee correspondingly.

Reversed Phase HPLC used to determine chemical purity:

Column: Waters Symmetry C18, 3.5 micron particles, 4.6×75 mmMobile phase A: 0.1% TFA in waterMobile phase B: 0.1% TFA in acetonitrileGradient: 5% B to 100% B in 16 minutes, return to initial conditions at16 minutes.Detector wavelength=280 nmInjection volume=5 microlitersRetention time: 7.87 minHPLC purity: 96.69%

Optical purity was determine by chiral HPLC:

Column: Chiracel OJ, 4.6×250 mm

Isocratic, 75% (0.2% phosphoric acid in water), 25% acetonitrileFlow: 0.75 mL/minDetector wavelength: 215 nmRetention time: 54.28 minChiral purity: 100% eeOptical rotation: [α]=−19.1° C.

A reported optical rotation for S-equol crystallized from aqueousethanol is [α]=−21.5° C. (The Merck Index, 1996, 12th edition, p 618).

LC-MS traces and spectra of the S-Equol product are shown in FIGS. 6Aand 6B, respectively.

¹H NMR and ¹³C NMR data appear below.

¹H NMR (300 MHz, CDCl₃, δ): 9.32 (s, 1H, OH), 9.21 (s, 1H, OH), 7.09 (d,2H, J=8.4 Hz), 6.86 (d, 1H, J=8.1 Hz), 6.72 (d, 2H, J=8.7 Hz), 6.30 (dd,1H, J=8.4 J=2.1), 6.21 (d, 1H, J=2.4 Hz), 4.15 (ddd, 1H, CH₂O, J=10.5Hz, J=1.80 Hz), 3.88 (t, 1H, CH₂O, J=10.2 Hz), 3.00 (m, 1H, CH), 2.78(m, 2H, CH₂). ¹³C NMR (75 MHz, CDCl₃, δ): 156.515 (C7), 156.151 (C4′),154.557 (C9), 131.711 (C10), 130.134 (C8), 128.346 (C6), 115.321 (C3′),112.627 (C1′), 108.048 (C5), 102.547 (C2′), 70.309 (C2), 37.197 (C3),31.324 (C4).

The resulting S-equol product was then converted into the TMS derivateand the TBDMS derivative according to the methods described in theMethods section, in order to improve volatility of the S-equol compoundduring the mass spec analyses. The GC-MS traces and spectra of theTMS-derivative S-equol products are shown in FIGS. 9A and 9B,respectively. The GC-MS traces and spectra of the TBDMS-derivativeS-equol products are shown in FIGS. 9C and 9D, respectively.

Example 7 Enantioselective hydrogenation of bis-MOM dehydro-equol toMOM-protected R-equol((R)-7-(methoxymethoxy)-3-(4-methoxymethoxy)-phenyl chroman)

A solution of 14.02 g (42.69 mmol) of bis-MOM-dehydroequol and 0.650 g(0.378 mmol, 0.88 mol %) of((4S,5S)-(−)-O-[1-Benzyl-1-(5-methyl-2-phenyl-4,5-dihydro-oxazol-4-yl)-2-phenylethyl]-diphenylphosphinite-(1,5-COD)-iridium(I)tetrakis-(3,5-bis-trifluoromethyl)-phenylborate(purchased from Strem) in 300 mL of dichloromethane was placed in a 2 Lglass reactor equipped with a magnetic stirrer, thermocouple, gas inlettube and a pressure relief valve. The air was replaced with nitrogenfollowed by hydrogen purge, and a 60 psig hydrogen pressure wasmaintained. The reaction mixture was monitored with TLC (R_(f)=0.26 forstarting bis-MOM-dehydroequol, greenish spot with PMA on hot plate, andR_(f)=0.28 for bis-MOM-equol, a purple spot with PMA, in ethylacetate/hexane=1:9). The reaction was kept at 60 psig hydrogen pressureand room temperature for 35 min until all starting material is consumed.Hydrogen was immediately replaced with nitrogen and clear red solutionwas quenched as quickly as possible with a cold ammonium chloridesolution (30 g of NH₄Cl, 50 g ice in 300 mL of water). The organics wereextracted with dichloromethane (2×200 mL), combined organic phases werewashed with 300 mL of water and dried over sodium sulfate. Solvent wasremoved on rotavap and a red oil was purified on silica gel plug (400 gof SiO2) using ethyl acetate/hexane=2:8 (2 L) and 3:7 (1.5 L) mixturesas an eluent to give a 14.00 g (99.2% yield) of a yellowish oil whichslowly crystallized to an off-white solid with mp 37-38° C. Thismaterial was used without any purification in the next step.

GC-MS traces and spectra of the product are MOM-protected R-equol shownin FIGS. 7A and 7B, respectively. LC-MS traces and spectra of theMOM-protected R-equol product are shown in FIGS. 7C and 7D,respectively.

The ¹H NMR (300 MHz, CDCl₃, δ) and ¹³C NMR (75 MHz, CDCl3, δ) weresimilar to bis-MOM-S-equol.

Example 8 Deprotecting the bis-MOM-R-Equol to R-Equol((R)-3-(4-hydroxyphenyl)-chroman-7-ol)

A solution of 14.0 g (42.37 mmol) of (R)-bis-MOM-equol in 70 mL of 1:1mixture of CH₂Cl₂/MeOH was placed in a 0.5 L 3-neck round bottom flaskequipped with a magnetic stirrer, thermocouple, cooling ice bath andnitrogen line. A total of 80 mL of 10 wt % solution of HCl in MeOH(175.3 mmol, 4.1 eq.) was slowly added to pre-chilled (6.3° C.) solutionof bis-MOM-equol. The reaction mixture was allowed to warm up to roomtemperature and monitored by TLC until all starting material isconverted to R-equol (R_(f)=0.58 for bis-MOM-equol, 0.28 formono-MOM-equol, and 0.10 for R-equol in ethyl acetate/hexane=2:8). After6 hours at room temperature a complete deprotection was observed.Solvent was removed under reduced pressure and precipitated solid (28.3g) was treated with 325 mL of ice-cold water, extracted with ethylacetate (2×200 mL). Combined organic phases were washed with dilutedsodium bicarbonate (10 g NaHCO₃ in 200 mL of water). Organic layer wasdried over sodium sulfate and solvent was removed on rotavap to yield12.5 g of an off-white solid. This solid was passed through silica gellayer (200 g of silica) using EtOAc/hexane=3:7 mixture (3 L) as aneluent. A solvent volume was reduced up to about 100 mL, and 10 g ofcharcoal was added. The resulted mixture stirred for 10 min, charcoalwas filtered off, and hexane was added to the filtrate causingprecipitation of the product. The precipitated material was filteredoff, washed with hexane (2×50 mL) and dried in a vacuum oven to yield4.25 g (41% yield) of R-equol as a white solid with mp 163° C. Noattempt was made to recover an additional amount of R-equol from motherliquor. Chemical and optical purity were determined using the samemethods described for S-equol and were found to be 98.31% (retentiontime 7.82 min) and 98.6% ee (retention time 57.82 min).

LC-MS traces and spectra of the S-Equol product are shown in FIGS. 8Aand 8B, respectively.

The ¹H NMR (300 MHz, CDCl₃, δ) and ¹³C NMR (75 MHz, CDCl3, δ) weresimilar to S-equol.

The resulting R-equol product was then converted into the TMS derivateand the TBDMS derivative according to the methods described in theMethods section. In order to improve volatility of the R-equol compoundduring the mass spec analyses. The GC-MS traces and spectra of theTMS-derivative R-equol products are shown in FIGS. 10A and 10B,respectively. The GC-MS traces and spectra of the TBDMS-derivativeR-equol products are shown in FIGS. 10C and 10D, respectively.

Example 9 Synthesis of 2,3-dehydroequol intermediate product

60 g bis-MOM 3,4-dehydroequol was hydrogenated to enantioselective equolin accordance with Example 6, using 1 mol % of the iridium catalyst and60 psig hydrogen pressure. During the hydrogenation, the reactionmixture was periodically sampled and analyzed by GC-MS (HP 5890 and MS5972, with column DB-5MS, 30 m length, 0.25 mm OD, 0.25 micrometer film,He carrier gas, and flow rate 1.7 mL/min. The temperature was programmedas follows: 50 C for 1 min., raising the temperature by 20 C/min to 300C, and then held at 300 C for 5 min. Total run time is 18.5 min.Retention time in the GC-MS is 15.77 min. for the equol product, and16.41 min. for the starting material dehydroequol.

During the run time, an intermediate product peak was observed by GC-MS,distinct from the starting material 3,4-dehydroequol and the productS-equol. The intermediate product had the same molecular weight (MW) asthe starting material. A reasonable assumption of a synthesis routeleads to the conclusion that the intermediate material is2,3-dehydroequol. The following mass ratios in the sample and thedetermined molecular weights are presented below in Table 1 for thestarting material (3,4-dehydroequol), the intermediate material(2,3-dehydroequol), and the finished product (S-equol).

TABLE 1 Weight ratio Time: 3,4 2,3 ↓ dehydroequol dehydroequol S-equolMW: → 328 328 330 Mass ratio: 0 100 0  0 20 45 16  38 60 6 0.6  93 110 00  100* *including trace product decomposition material

Example 10 Deprotection of bis-MOM 3,4-dehydroequol[3-(4-Hydroxyphenyl)-2H-chromene-7-ol]

A solution 0.42 g (1.28 mmol) of7-methoxymethoxy-3-(4-methoxymethoxy-phenyl)-2H-chromen(bis-MOM-dehydroequol) in 20 mL of dichloromethane was mixed with 8 mLof 10% HCl/MeOH (17.3 mmol, 13.5 eq.) at 0° C. The resulting solutionwas kept at this temperature for two days and the reaction was monitoredby TLC until all starting material disappeared (R_(f)=0.65 forbis-MOM-dehydroequol and R_(f)=0.14 for dehydroequol inEtOAc/hexane=3:7). The reaction mixture was concentrated on rotavap, theresidue diluted with ethyl acetate (50 mL) and quenched with saturatedsodium bicarbonate (200 mL). The organic layer was separated, and theaqueous phase was extracted with ethyl acetate (2×100 mL). The organiclayers were combined, washed with brine (50 mL), dried over sodiumsulfate and concentrated in vacuum to give 0.32 g (104% yield) of pinksolid. This solid was dissolved in a minimum amount of ethyl acetate andpurified on silica gel plug using ethyl acetate/hexane=1:2 and 1:1.5mixture as an eluent. Fractions containing dehydroequol were collectedand concentrated to give a white solid. The isolated solid was dissolvedin ethyl acetate (about 15 mL), filtered and hexane (about 15 mL) wascarefully added to the solution resulting in crystallization. Theprecipitated solid was filtered, washed with hexane (2×20 mL) and driedunder nitrogen to give 0.139 g (45% yield) of dehydroequol as a whitesolid with a faint pink tinge. The second crop (80 mg) was recoveredfrom the filtrate to give a total of 0.219 g (71% isolated yield) ofdehydroequol product (7-hydroxy-3-(4-hydroxyphenyl)-2H-chromene).

¹H NMR (300 MHz, DMSO-d₆, δ): 5.02 (s, 2H, CH₂), 6.25 (bs, 1H, C═C—H),6.33 (dd, 1H, J=1.8 Hz, J=8.4 Hz, ArH), 6.75 (s, 1H, ArH), 6.77 (d, 2H,J=8.7 Hz, ArH), 6.93 (d, 1H, J=7.8 Hz, ArH), 7.33 (d, 2H, J=8.4 Hz,ArH), 9.58 (bs, 2H, OH). ¹³C NMR (75 MHz, DMSO-d₆, δ): 66.264, 102.296,108.525, 114.739, 115.426, 116.688, 125.587, 127.124, 127.254, 127.448,153.691, 157.016, 158.019.

1. A method for preparing enantioselectively an enantiomeric chromane(compound (I)):

wherein each R⁴, R⁵, R⁶, R⁷ is independently selected from the groupconsisting of H, OH, phenyl, aryl, alkyl, alkylaryl, arylalkyl, OR⁸,OC(O)R⁸, OS(O)R⁸, thio, alkylthio, mercaptal, alkylmercaptal, amino,alkylamino, dialkylamino, nitro and halo, and where R⁸ is alkyl andalkylaryl; and R¹, R2, and R³ is independently selected from —R⁴ and

wherein each R⁹, R¹⁰, R¹¹, R¹², and R¹³ is independently selected from Hand R⁴; comprising the steps of: 1) providing a chromene compoundselected from:

2) hydrogenating the chromene in the presence of an Ir catalyst having achiral ligand shown as compound (V):

to form the corresponding chromane; wherein each of Y and X isindependently selected form the group consisting of S, O and N, and eachR¹⁴ and R¹⁵ is independently selected from the group consisting ofalkyl, aryl, phenyl, alkylaryl, and arylalkyl.
 2. The method accordingto claim 1 wherein the step of providing a chromene compound furthercomprises the step of protecting any hydroxyl substituents among R¹, R²,R³, R⁴, R⁶, or R⁷ with a hydroxyl protecting group.
 3. The methodaccording to claim 2 wherein after the step of hydrogenating, theprotecting group is removed by acidifying the product.
 4. The methodaccording to claim 1 wherein, when the carbons in the 4 and 5 positionsof the ligand (III) are both S configuration, the resulting chiralcarbon of compound (VI) is R configuration, and wherein when the carbonsin the 4 and 5 positions of the Ir catalyst (III) are both Rconfiguration, the resulting chiral carbon of compound (VI) is Sconfiguration.
 5. The method according to claim 1 wherein theenantiomeric chromane has the structure wherein R¹, R³, R⁵, and R⁷ andH, R² is phenol, and R⁶ is OH.
 6. The method according to claim 1wherein X is O, and Y is N.
 7. The method according to claim 1 whereinR¹⁴ is phenyl and R¹⁵ is methyl.
 8. The method according to claim 1wherein the Ir catalyst comprises an Ir-ligand complex shown as complex(XV) and a counterion shown as compound (XVI):


9. The method according to claim 1 wherein the step of hydrogenating isconducted at 0-150 psig, at a temperature of from about 5° C. to aboutroom temperature, and with a solvent selected from a lower alkyldihalide solvent.
 10. The method according to claim 1 wherein theconcentration of the chiral Ir catalyst is between 0.1 to 10 mol %relative to the chromene.
 11. A method for preparing enantioselectivelyan enantiomeric equol, and analogs thereof, comprising the steps of: 1)providing a chromene selected from:

wherein Z is H or PG, and PG is a hydroxy protecting group; and 2)hydrogenating the pchromene in the presence of an Ir catalyst having achiral ligand (compound (V)):

to form an enantiomeric equol (compound (VIb))

and analogs thereof, wherein each of Y and X is independently selectedform the group consisting of S, O and N, and each R¹⁴ and R¹⁵ isindependently selected from the group consisting of alkyl, aryl, phenyl,alkylaryl, and arylalkyl.
 12. The method according to claim 11 whereinthe chiral ligand is compound (IX):


13. The method according to claim 11 wherein the step of hydrogenatingis conducted at about 0-150 psig, at a temperature of about 5° C. toabout room temperature, and with a solvent selected from dialkyldihalide solvent.
 14. The method according to claim 11 wherein theconcentration of the Ir catalyst is about 0.1 to 5 mol % relative to thechromene.
 15. The method according to claim 11 wherein the protectedchromene is made by dehydrating a chroman-ol compound.
 16. The methodaccording to claim 15 wherein the chromal-ol is made by reducing achroman-one or a chromen-one.
 17. A method of preparingenantioselectively an enantiomeric equol, and analogs thereof,comprising the steps of: 1) reducing a 3-phenyl-chromen-4-one to a3-phenyl-chroman-4-one; 2) reducing the 3-phenyl-chroman-4-one to a3-phenyl-chroman-4-ol; 3) dehydrating the 3-phenyl-chroman-4-ol to a3-phenyl-chromene selected from 3-phenyl-3,4 chromene and 3-phenyl-2,3chromene; and 4) hydrogenating the 3-phenyl-chromene in the presence ofan Ir catalyst having a chiral ligand:

to form enantioselectively an enantiomeric equol (compound (VIb)),

wherein Z is H or PG is a hydroxy protecting group; wherein each of Yand X is independently selected form the group consisting of S, O and N,and each R¹⁴ and R¹⁵ is independently selected from the group consistingof alkyl, aryl, phenyl, alkylaryl, and arylalkyl, and wherein PG is ahydroxyl protecting group.
 18. The method according to claim 17 whereinthe 3-phenyl-chromen-4-one is selected from the group consisting ofdaidzein and formonenetin and mixtures thereof.
 19. The method accordingto claim 17 wherein R¹⁴ is phenyl and R¹⁵ is methyl.
 20. The methodaccording to claim 17 wherein PG is methoxy methyl.